1. Technical Field
The invention relates to theft deterrent systems for commercial vehicles and more particularly to a theft deterrent system integrated with existing vehicle control systems.
2. Description of the Problem
Medium and heavy duty trucks often transport valuable or hazardous cargo. This makes these vehicles targets for thieves. Unfortunately, truck electrical wiring is relatively simple compared to passenger cars. In addition, most medium and heavy duty trucks do not have locking steering columns or transmissions. Not having to defeat such devices reduces the time and effort required of thieves to steal a medium or heavy duty truck. It is a relatively simple matter on many vehicles simply to “slim-jim” the door lock and hot wire the key switch, defeating the basic security procedure of removing the ignition key and locking the vehicle.
After-market devices designed to interrupt the ignition or engine crank circuit are known. These devices may require a hidden switch be depressed or some electrical feature such as headlights or the turn signal be switched on before engine cranking is tried. Experienced thieves and other well informed criminals can normally spot such systems quickly as they are not integral to the truck electrical system. This factor contributes to making the devices easier to defeat. Where such a device malfunctions due to failure of the device or poor installation, it can render the vehicle inoperative and make it difficult for regular service personnel to correct on account of lack of familiarity with the device. Such devices can prevent or delay emergency workers from starting and moving a vehicle, as may be necessary where a vehicle hauling flammable cargo is in the vicinity of open flames.
One example of a third party, after-market device, which provides an add-on circuit module, includes a series of switches into which the driver must type a numeric code before the park brake is released. If this is not done the engine is stopped by opening the ignition switch power feed through a relay. This device includes operational modes that are problematic. For example, the anti-theft code must be reentered every time the park brake is released or the engine is restarted. A flustered driver may be temporarily unable to reenter the code under time pressure.
Any theft deterrent system which simply prevents the engine from cranking should also be capable of maintaining memory through the low voltages associated with engine cranking. This can require an expensive power supply.